The invention relates to a programmable semiconductor device comprising a semiconductor body provided with a comparatively weakly doped surface region of a first conductivity type which is covered by a dielectric layer on which a number of semiconductor regions of a second, opposite conductivity type and a comparatively high doping concentration are provided side by side, each semiconductor region in combination with the subjacent portions of the dielectric layer and the surface region forming a programmable element which is programmed in that a sufficiently high voltage is applied between the semiconductor region and the surface region, so that owing to breakdown across the dielectric layer a zone of the second conductivity type is formed in the surface region, which zone is conductively connected to the semiconductor region and forms a rectifying junction between the semiconductor region and the surface region. The invention also relates to a programmable semiconductor memory comprising such a semiconductor device.
A semiconductor device of the kind described above is known from, inter alia, U.S. Pat. No. 4,881,114. In this known device, the semiconductor body is formed by an n-type silicon substrate in which locally a p-type surface region is provided in the form of a diffused zone. The dielectric layer is formed, for example, by a thin composite layer of silicon oxide, silicon nitride, and silicon oxide. On this layer are formed semiconductor regions of comparatively strongly doped n-type polycrystalline silicon, called poly for short hereinafter. The dielectric layer forms an anti-fuse which makes a transition from non-conducting in the non-programmed state to conducting during programming. During programming, a sufficiently high voltage is applied between the p-type surface region in the semiconductor body and an n-type poly region, whereby breakdown takes place locally in the dielectric layer and a pinhole is formed in the dielectric layer. Owing to heat generation, n-type dopant diffuses from the poly into the p-type surface region, so that an n-type zone is created in this region which forms a pn junction with the surface region. Arranged in a matrix, these elements may form a programmable memory (PROM) or a programmable logic array (PLA). An important advantage of the use of such programmable elements is, as also stated in the cited US Patent, that extremely high densities can be obtained.
It was found in practice that, for example, in memories built up from these programmable elements strong leakage currents often occur between adjoining diodes, i.e. for example, greater than 1 nA. Among the disadvantages of these leakage currents is that programming proceeds with difficulty owing to voltage losses and also that the dissipation has an undesirably high value.